1. Forensic Crime Science
Fire Debris Analysis
Forensic Crime Science

2. Fire
Arson - The crime of maliciously, voluntarily, and willfully setting fire to the building, buildings, or other property of another or of burning one's own property for an improper purpose, as to collect insurance.
Arson – The crime of starting an illegal fire.

3. Transfer Types of Heat
Conduction Convection Radiation Direct Flame Contact

4. Fire: rapid oxidation with evolution of heat and light.

5. Four components of fire:
Fuel
Heat
Oxygen
Uninhibited chemical chain reaction

6. Four components of fire:
Fuel: can be solid, liquid or gas
Fuel can only consumed in the vapor state
Therefore, solids and liquids must first be “vaporized”
Burning takes place at the surface of solids and liquids.

7. Four components of fire:
Heat: Temperature
Oxygen: found in air; can be used up in closed in spaces.
Chemical Chain Reaction must:
The oxidation reaction (burning) must produce enough heat to maintain burning
The fuel mass must be vaporized and drawn up into the flame.

8. Who investigates the fire?
Cause of Fire:
Natural
Accidental
Unintentional
Intentional
Who investigates the fire?
Often, the Fire Department will have an investigative team to determine the cause/origin of a fire. (major events = ATF)

9. Fire Debris
Fire debris is submitted to laboratories for analysis by the fire marshal, crime scene investigators, forensic scientists, and insurance investigators.
Investigators determine the best locations at the scene to collect samples, based on suspicious details.

10. Suspicious Circumstances
The presence of:
a)combustible
b) increase the rate of combustion
These are frequently detected by canines trained to detect ignitable liquids by smelling the fire debris.
Investigators can also detect the presence of these liquids from pour patterns that remain on the burnt substrate after the fire.

11. Pour Patterns
Pour patterns often are characterized by intermixed light, medium, and heavy burning in a puddle shape that corresponds to the shape of the original pool of the ignitable liquid.

12. Other indicators of ignitable liquid
unnatural flame movement (downward or too fast)
gapping of wood or floor seams (caused by pooling of liquid)
damage with no identifiable point of origin
burned out flooring beneath appliances and furniture
Inverted cone shaped burn patterns on vertical surfaces

13. Fire Investigation: First the point of origin is determined:
Where the fires starts
Usually contains the most damage.
Once point of origin is determined, the cause of the fire is determined.

14. Fire Debris Samples
Sample areas likely to contain traces of ignitable liquid:
lowest regions of burned area
insulated areas within the pattern
porous substrates in contact with the pattern
cloth
paper products
wood
seams or cracks
lightly burned edges of the pattern

15. What evidence can be collected?
Paper/Trash – not much evidence
Accelerant – rapid start
Chemical device (road flares, propellant)
Electronic device for delayed ignition
Unburned portions of chemical and electronic devices may be left behind.

16. Collection of Fire Debris
Once an appropriate area has been identified for sampling, samples are collected for later analysis.
Samples are collected in a tightly sealed container (glass jar or metal can).

17. Collection of Evidence
Even in a large fire, accelerant residues of flammable liquids may be left behind.
Common: gasoline, kerosene, fuel oil
Rarer: alcohol, paint thinner
Unusual burn pattern may suggest use of liquid accelerant.

18. Collection of Evidence
Along with sample from point of origin, a control sample should be collected. (material from a different room/location)
Carpet fibers (synthetics) may be “petroleum” based.
Obviously, evidence collection documented with photos, sketches, etc.

19. Collection of Evidence
Accelerant remains can be detected by tracing the point of origin or canine use.
Object containing accelerant must be packaged in air tight container.

20. Containers for Evidence
Metal cans: airtight, but old cans might rust
Glass Jars: rubber or glued liners may interfere with results.
Special airtight plastic evidence bags: must be properly sealed

21. Collection of Samples Sample should fill 2/3 of the container.
Top 1/3 of container is used for sampling headspace.

22. Passive Headspace Sampling
In passive headspace sampling the container is heated to volatilize any ignitable liquids remaining in the sample.
A Activated charcoal is suspended in the headspace
to absorb the volatilized liquid.
The charcoal is then removed from the sample container and the liquid is removed from it by solvent extraction.

23. Solvent Extraction
Carbon disulfide is frequently used in solvent extraction because it produces excellent desorption of most accelerants.
It also produces a low detector response when analyzed by a gas chromatograph using a flame ionizer detectorr.
Unfortunately, carbon disulfide is a health hazard because it can cause nervous system damage.

24. GC-MS
After the solvent is extracted it is analyzed with a gas chromatograph and a mass spectrometert(GC-MS).
The liquid is injected into the GC and carried through the instrument by an inert carrier gas (called the mobile phase).
The liquid then permeates a column (long thin tubing) which binds the liquid to a polymer coating on the inside (called the stationary phase). This separates the liquid components by volatility.

26. Analysis of Accelerants
Gas Chromatography separates components and Mass Spectrometry identifies the components.

27. GC-MS More volatile components move faster through the column.
The components come off of the column separately during the elution step and enter the mass spectrometer.
The mass spectrometer separates each component based upon the mass-to-charge ratio of their particles.
The mass spectrum of the sample is then compared to a library of known compounds to identify the compound in the sample.

28. Presumptive Testing
GC-MS analysis can be time consuming and expensive.
A presumptive test can be performed quickly in the field to indicate the presence of an ignitable liquid.
Colorimetric gas detection tubes are used for this purpose

29. Presumptive Testing
Colorimetric gas detection tubes are filled with a compound designed to react with a specific compound of interest (gasoline, diesel fuel, etc.)
To perform the test, both ends of the glass tube are broken off.
Air from the scene is drawn through the tube with a pump

30. Presumptive Testing
In the presence of specific vapors, the compound within the tube will change color.
The concentration of the compound may be estimated but this technique is not very accurate.

31. Presumptive Testing
If the presumptive test is positive, then samples will be collected for GC-MS analysis.
In some labs, this is used for preliminary screening of samples.

33. http://www.cbsnews.com/videos/arson-investigation/ criminal homicide arson
fire investigations
anatomy of a fire scene
job of fire investigator